The 'back' arrow you see at the top left of the menu bar in PS touch only saves what you've been working on--or have modified (also as 'save as') as a .psdx file. This can of course be opened again in Touch, or exported via the Cloud (and by email) to your desktop if you want to work on it there.

From the main menu view, you can use the folder with an arrow, to upload to the cloud, save projects to the Gallery (as jpg ot png files), or share (in different file formats) via email, gmail, evernote, bluetooth, or send to other photo apps (these are the options on my tablet).